This invention relates to an engine block heater and particularly to a technique in such a block heater for coupling the clamping screw to the rear clamping member.
Engine block heaters are required for cold climatic conditions and generally comprise a heater body for mounting in an aperture in the wall of the engine block. The aperture is generally circular so that the heater body is similarly circular in front elevation with a front face for facing out of the engine block and a rear face for facing inwardly into the engine block. The front face includes a flange for surrounding the aperture and a locating means or rear clamping member is located on the rear face for engaging the inside surface of the wall of the block.
In some embodiments the locating means comprises simply a transverse plate which is rigid and is carried upon a loose screw which extends through an aperture in the heater body so that rotation of the screw by actuation of the head of the screw presented at the front face causes the plate member to be drawn toward the rear face to engage the inside surface of the block in a clamping action.
In other embodiments, the rear locating means comprises a generally V-shaped body with a pair of rearwardly and outwardly diverging legs which commence at a position with a relatively narrow angle of the V and are then pushed outwardly into engagement with the inside surface of the block by a pressure plate which is squeezed against a rear face of the legs by forward movement caused by cooperation with the loose screw.
In both embodiments it is necessary to ensure that reverse rotation of the screw, that is in a direction to move the locating means away from the rear face, does not allow the locating means to be released from the screw and thus dropped into the interior of the engine. The conventional technique which is used to generate the five or six pounds of torque resistance desirable in this arrangement is simply to crimp the last three or four turns of the thread of the screw so that the female screw threads of the locating member cannot pass over the crimped or deformed male threads of the screw.
Examples of block heater designs are shown in U.S. Pat. No. 3,766,356 (Feldmann), and in Canadian patents 1,096,918 (Brinkhof), 1,095,355 (Kendall), 854,325 (Windsor) and 1,192,248 (Brinkhof). None of these patents discuss in any way this necessity to prevent release of the locating member from the screw. However, in the commercial embodiments manufactured as shown in these patents or otherwise, the above described crimping technique is generally used,
The crimping technique is simple and inexpensive and is therefore substantially universally used. However, careful analysis of the design by the present inventors has realized that there are a number of disadvantages in use of this technique.
Firstly, the crimping technique necessarily requires that three or four turns of the male thread of the screw remain exposed at the back of the locating member. This necessarily therefore increases the dimensions of the structure since the screw length must be increased to accommodate these additional threads. In some arrangements now necessary for the smaller engines currently being manufactured, it is difficult to accommodate this increased dimension of the block heater.
Secondly, it is necessary to have access to the end turns of the screw to effect the crimping action. This requires the screw to be clamped from two sides and in some designs now desirable this access may be limited or unavailable. Thus in many designs, as shown for example in the above Feldmann patent, the block heater element is formed in a U-shape which is bent at right angles so that a main portion thereof lies parallel to the rear face of the heater body. In arrangements where there is very limited space for the element, it is necessary for the distance between the main portion of the element and the rear face to be considerably reduced. Thus the end of the screw may be located between the legs of the element and thus unavailable for the crimping action.
In a further known technique, a protruding end of the screw is impacted in an axial direction with a pointed impact tool. This impact creates a small indent and attempts to force an end part of the screw radially outwardly and form a bulged section at the end of the screw. This bulged section resists passage of the locating member beyond the end of the screw. There are a number of disadvantages to this technique. Firstly the impact causes high axial loading on the screw which can cause damage to or buckling of the screw. Secondly the screw must still project above the rear surface of the locating member so that it is not possible to form a restriction on the screw which is flush with the rear surface of the locating member. Thirdly the back-off torque is not fully reliable as the amount of deformation is not controlled and hence is not fully consistent.